1. Field of the Invention
The present invention relates to a method for assessing irradiation intensity of a laser beam irradiated onto an object, an irradiation intensity assessment apparatus used under this method, and a laser beam irradiation system.
2. Description of Related Art
Laser beams are used in various fields such as for medical treatment and processing materials and the like. As an ophthalmological laser irradiation apparatus, for example, such has been known that an operator irradiates an excimer laser beam using an apparatus to ablate an epithelium and a corneal stroma of a patient's eye to change corneal curvature for correcting a refractive error such as myopia or to ablate an affected area of a corneal surface. As for this type of the apparatus, it is considered important to arrange the apparatus so that ablation depth is approximately uniform on an object to be irradiated. European Patent Application publication No. EP1040797 corresponding to Japanese Patent Application Unexamined Publication No. 2000-279440 should be referred, wherein the present applicant discloses a laser irradiation apparatus configured in such a manner that laser beam irradiation density within an ablation region is changed so that the operator ablates an object approximately uniformly using the apparatus.
Incidentally, although adjustment for accomplishing approximately uniform ablation is carried out at the time of manufacturing a laser irradiation apparatus, an ablation depth on the object to be irradiated may change when optical elements are set at a site for installing the laser irradiation apparatus. This change may be caused by an influence of a delicate alignment adjustment of optical axes. The ablation depth on the object to be irradiated may also change because of deterioration due to a change over time in an optical element disposed in an irradiating optical system. Thus, at the site for installing a laser irradiation apparatus, prior to actual laser irradiation on an object to be processed (treated), it is necessary to irradiate a laser beam on a reference object for assessment and adjust irradiation intensity of the laser beam based on the examination of the ablation depth.
Conventionally, as for a simplified method for examining an ablation depth, such has been conducted that after irradiating a laser beam on a transparent polymethyl methacrylate (PMMA) plate in a certain irradiation condition and ablating the plate, a change in a refractive power on the PMMA plate is read using a lens meter. Further, detailed data on the ablation depth are obtained by analyzing the ablated PMMA plate using a three-dimensional shape analyzing apparatus.
An examination using a lens meter is relatively easily carried out at the site where a laser irradiation apparatus has been installed. However, it merely gives general information about the ablation depth, and it does not give the details.
On the other hand, when a three-dimensional analyzing apparatus is used, the apparatus is large-scale and pricey, and its transportability is low. Therefore, there may be occasions when using the three-dimensional analyzing apparatus is not easy at the site for installing a laser irradiation apparatus.